IN THE EARLY 1960s, a doctor wrote a book called "Calories Don't Count," and the government tried to put him in jail for fraud. Agreed, calories do count, but like the pigs in Orwell's "Animal Farm," some calories may count more than others. The egalitarian calorie theory, the mainstay of dieting advice in recent memory, is being challenged by a revolutionary new idea: that all calories, once in the body, are not equal in fattening value. The research is recent and the findings tentative, but already it points to new ways we should eat to lose weight -- or gain weight, if that's a concern.

First, the current theory: All calories will fatten you up the same way. It takes 3,500 calories of any kind of food to add a pound of weight. And 3,500 calories' worth of deprivation to take it off. A calorie of carrot has the same impact in the body as a calorie of salad oil. Therefore it doesn't matter what kind of food you eat, as long as you count calories. The theory is predicated on the measurement of calories in a pristine laboratory. The assumption is that your body will absorb and metabolize all foods identically.

Few researchers have looked to find out what happens to that food inside the body. When two researchers at the Veterans Administration Medical Center in Minneapolis did investigate recently, they came up with surprises. They studied how 10 people absorbed the fat from three foods -- peanuts, peanut butter and peanut oil. Here's what they found: In eating 100 calories' worth of fat in peanuts, peanut butter and peanut oil, the average person will absorb nearly all the fat calories in the peanut oil, 94 calories in the peanut butter and 82 calories in the whole peanuts. One person in the study absorbed only 68 percent of the fat from whole peanuts.

The message is probably as clear to you as it was to the researchers: You can't get fat on what you don't absorb. Therefore, If you want to lose weight, you're better off eating 100 calories of peanuts than the same number of calories of peanut butter or peanut oil. Dr. Allen S. Levine, a nutritionist and one of the researchers, thinks the reason is common-sense simple. Since neither your teeth nor digestive system is as efficient as a food processor in liquifying food, some chunks pass through and out of the intestines instead of being soaked up to make new fat cells. On the other hand, liquids like oils pose no such problem: They're a cinch to sink right into the intestine walls and be carried away to manufacture fat.

Whether this is true for foods besides peanuts -- that the coarser their consistency the less fattening they are -- is unknown. Dr. Levine can't say so scientifically because he hasn't tested other foods. He is now doing the same experiment with corn. But he believes that in practice it is true. He counsels his overweight clients to eatless highly processed foods and more whole, natural foods, on the theory they won't digest them as well and will lose more weight than expected from merely counting calories. That means whole-wheat bread instead of white bread, apples over applesauce and apple juice, high-fiber, whole-grain cereals such as bran instead of cereals fabricated from wheat flour. In general, the whole food instead of its mashed up or purified derivative. Foods that are closer to nature than to the factory.

And there's more reason for that advice. Dr. Levine's study also showed that you can wash away some of the calories from highly processed fatty foods by eating more high-fiber foods. People in his study absorbed about 3 percent less fat from peanut butter and peanut oil when they also ate lots of high-fiber vegetables. Dr. Levine speculated that perhaps the high-fiber foods pushed the fatty foods through the intestines faster, giving them less time to get into the system, or metabolically changed the ability of fats to be absorbed.

Dr. Levine also discovered in the medical literature studies showing that you feel less hungry when you eat the same number of calories from an apple or whole-grain bread than from applesauce or apple juice or white bread. Part of the reason is the bulk, but another part, he says, is that it takes 20 times longer to eat an apple than to drink a glass of apple juice. During that interval, the stomach has time to signal the brain's appetite center that you're getting full. That doesn't happen when you are able to down a lot of calories rapidly.

As you may have notice, this theory of dieting with whole, natural foods pushes you further away from the current rage of high-protein diets. And there may be another justification for that. A recent University of Virginia study on rats showed that the more protein and less complex carbohydrates they ate, the fatter they got -- even though they ate the same number of calories. Rats on a 25 percent protein/65 percent carbohydrate diet gained twice as much weight as rats on a 5 percent protein/85 percent carbohydrate diet. The researcher, Dr. Patillo Donald, concluded that protein adds more weight than could be accounted for by calories. She, like Dr. Levine, advises dieters to eat more fruits, vegetables and grains -- in other words, complex carbohydrates.

The last word on diets is surely not in. But it seems clear there's more to dieting than counting calories. It is a far more complex subject, needing more sophisticated research. Calories undoubtedly do count, but it appears so far that by eating more food in its original, close-to-nature state, you can make them count for less.